US3643757A - Flexible skirts for surface-effect machines - Google Patents

Abstract

A skirt for peripherally confining a fluid cushion for a surface-effect machine, comprising a fluidtight flexible sheet encircled by a plurality of transverse hoops made of a material less deformable in the peripheral direction of the skirt than that of the sheet, whereby the said hoops cooperate with the said sheet in such a manner that the height of the skirt automatically decreases when the pressure of the cushion increases.

Description

States atet Delamare Feb, 22, 1972 [54] FLEXIBLE SKIRTS FOR SURFACE- EFFECT MACHINES [72] lnventor: Guy Robert Delamare, Les Iris, Herblay,1 ranoe Societe dEtudes et de Developpement des Aeroglisseurs Marins Terrestres et Amphibies S.E.D.A.M., Paris, France 22 Filed: May 7,1969

21 Appl.No.: 822,595

[73] Assignee:

[30] Foreign Application Priority Data May 9, 1968 France.... ..15 1208 [52] US. Cl ..180/l27 [51] Int. Cl ..B60v 1/16 [58] Field ofSearch ..180/127,124, 121

[56] 1 References Cited UNITED STATES PATENTS 3,078,940 2/1963 Rolle ..180/l27 3,174,573 3/1965 Chaplin ..180/12l 3,182,739 5/1965 COckerell 1 80/1 18 3,339,657 9/1967 Benin et al. ....180/127 3,340,943 9/1967 Hirsch ....180/1 18 3,414,075 12/1968 Bertin..... 1 80/121 3,513,933 5/1970 Faure ....l80/l21 3,258,080 6/1966 Williams et al. ..180/l27 3,388,766 6/1968 Bertin ..l80/127 3,416,627 12/1968 Francis et al. ....180/127 3,482,645 12/1969 Bertin et a1. ....180/124 3,511,331 5/1970 Laundry ..l80/l27 Primary ExaminerA. Harry Levy Attorney-Stevens, Davis, Miller & Mosher [57] ABSTRACT A skirt for peripherally confining a fluid cushion for a surfaceeffect machine, comprising a fluidtight flexible sheet encircled by a plurality of transverse hoops made of a material less deformable in the peripheral direction of the skirt than that of the sheet, whereby the said, hoops cooperate with the said sheet in such a manner that the height of the skirt automatically decreases when the pressure of the cushion increases.

3 Claims, 16 Drawing Figures PATENTEU FEB 2 2 I972 SHEET 1 0F 5 PATENTEUFEBZZ I972 3,643 ,757

SHEET 2 OF 5 FIG. -'7

FIG. :6

FLEXIBLE SKIRTS FOR SURFACE-EFFECT MACHINES This invention relates to skirts which peripherally confine the air cushions or other fluid cushions which support surfaceeffect machines.

It is known to form the wall of a skirt of this type from a deformable material which is kept in the stretched state by the positive pressure of the internal fluid or air so that the flexibility of the wall enables it to yield when passing relatively large obstacles. When the wall consists of an endless flexible skin or sheet which is circular in plan view, when inflated it normally assumes a shape of revolution about the vertical axis of the skirt. In some cases, however, it is advantageous to clinch the meridians of the skirt wall, for example by radially disposed webs so that when the skirt is inflated it assumes a multilobe shape, i.e., between the meridians clinched in this way it has a plurality of convex lobes whose sections through planes perpendicular to the skirt axis are circular arcs disposed in a gar- Iandlike fashion.

In known constructions, the height of the skirt in operation is generally fixed but it may alternatively be adjustable by means enabling it to be lifted on passing over large obstacles. It is also known, more particularly from U.S. Pat. No. 3,388,766, to incline the skirt wall inwardly by giving it a generally frustoconical shape whose free bottom sectionis smaller than the top section secured to the machine structure. The internal pressure forces thus produce a vertical component extending downwardly, which tensions the wall along its meridians so that the skirt tends to maintain its maximum height and immediately resumes it after having been lifted when passing over an obstacle. A skirt of this kind, which will hereinafter be referred to as a conical skirt may be circular or multilobed; it may consist ofa plurality offrustoconical sections of different degrees of conicity and may even include cylindrical portions.

According to the arrangement shown in FIG. of the above-mentioned Patent, a raisable skirt may have a flexible bottom portion and a bellous-type top section provided withrigid rings which prevent any increase in diameter or length of the bellows, the bottom ring being raisable by means of cables.

This invention relates to improvements for automatic and no longer controlled adjustment of the height of an inflatable flexible skirt, the skirt height decreasing automatically when the internal pressure increases. Nevertheless, of course, the skirts according to the invention may also includea controlled lifting system.

Known flexible skirts, whether circular or multilobed, conical or otherwise, are made from strong woven filiform elements which are juxtaposed or crossed in various ways. These elements which provide mechanical strength are covered with a flexible rubberlike material of any composition (natural or synthetic rubber, synthetic plastics, and so on) which provides impermeability. The resistant filiform elements are thus distributed in a diffused manner over the entire surface of the fluidtight sheet and are incorporated in its thickness.

In an inflatable flexible skirt, whether circular or multilobed, conical or otherwise, the main stresses due to the large radius of curvature of the wall appear in the horizontal direction or substantially horizontal direction, i.e., perpendicularly to the axis of revolution in the case of a cylindrical skirt or perpendicularly to the generatrices of the frustoconical portions of a conical skirt. As a result, in known inflatable skirts the internal pressure variations of the cushion mainly result in variations in the skirt diameter.

According to the invention, the strength function of the skirt is dissociated from the sealing function so that the said stresses are used to act on the skirt height. To this end, the skirt according to the invention consists of an impermeable flexible sheet or skin encircled by a plurality of spaced hoops disposed in substantially transverse planes with respect to the general direction of the skirt, the material of the said sheet having resistance to elongation in the peripheral direction less than that of the hoops and each of the sheet portions contained between two successive hoops being left free to undergo deformation in the said direction to an extent which depends on the pressure variations of the cushion so that the height of the skirt decreases automatically when the cushion pressure increases.

Thus in the case of a circular skirt, the sheet will be applied by the internal pressure against the hoops and will tension the latter. Each hoop will assume a position of equilibrium under pressure which will-impart a circular shape to it. Asit inflates, the sheet applied against the hoops will assume between the latter the shape of a plurality of superposed toroidal portions whose curvature in the vertical direction will increase as the internal pressure increases. The internal pressure variations will thus produce variations in the hoop spacing and hence variations in the skirt height.

This will result more particularly in an automatic dynamic stabilization, an improvement in the suspension of the surfaceeffect machine and a saving in mass, these being advantageous effects in respect of skirts of any shape, but more particularly when the invention is applied to a conical skirt as will be explained in detail hereinafter.

To obtain a multilobed skirt, the meridians of the wall do ,not have to be clinched by a continuous seam. It is only necessary to clinch appropriately selected points of the flexible hoops, and this can be done by means of cables.

The following description with reference to the accompanying drawings, which are given by way of example without limiting force, will clarify the details and advantages of the invention and the way in which it can be performed.

FIG. 1 diagrammatically illustrates a conical skirt according to the invention in elevation in the inoperative state;

FIG. 2 is a similar view to FIG. 1 showing the skirt under pressure;

FIG. 3 is a partial vertical section to an enlarged scale showing an embodiment of the hoops;

FIGS. 3a and 3b are similar views to FIG. 3 showing the deformation of the walls in the case of two different skirt pressures;

FIGS. 4 and 5 are similar views to FIG. 3, showing other embodiments;

FIGS. 6, 7, 8 and 9 are diagrammatic views similar to FIG. 2 showing other embodiments of conical skirts according to the invention when they are under pressure;

FIGS. 10 and 11 diagrammatically illustrate a tie system for clinching a multilobed skirt according to the invention, FIG. 10 being a vertical section on the line X-X in FIG. 11 and FIG. 11 being a section on the line XI-XI in FIG. 10;

FIG. 12 is a similar view to FIG. 10 showing a variant;

FIG. 13 is a partial section similar to FIG. 11 showing a detail of the clinching of a flexible hoop to an enlarged scale;

FIG. 14 is a partial section on the line XIV-XIV in FIG. 13.

The conical skirt 1 shown in FIG. 1 consists of a flexible sheet or skin secured to the structure 2 of a surface-effect machine and encircled by flexible hoops 3. The skirt is supplied with pressure fluid by known means (not shown) which form part of the surface-effect machine. FIG. 2 diagrammatically illustrates the inflated skirt. FIG. 3 is an enlarged-scale view of a portion of the skirt 1a between two hoops in the inoperative statewhile FIGS. 3a and 3b respectively illustrate this skirt portion inflated by a low pressure and a high pressure.

In the embodiment illustrated, the skirt 1 is circular so that, as already indicated, it will be applied by the pressure against the flexible hoops 3 which will assume a circular shape. Under the effect of the pressure the skirt 1 bearing against these hoops will assume its .form of revolution. The geometric definition of this form and its proportions will depend on the comparative values of the internal pressure and elasticity of I this sheet with respect to that of the hoops in the horizontal direction.

If the elasticity of the sheet were equal to that of the hoops, the skirt would assume a perfect conical shape and the hoops would be subjected to the same tension forces as the skirt. On the other hand, if the resistance of the sheet to elongation in the peripheral direction is negligible with respect to that of the hoops, each portion 1a contained between two hoops will assume a position of equilibrium which will give it the shape ofa portion ofa torus, and all the forces in the horizontal direction will be taken solely by the hoops. If the skirt were of the cylindrical type, each portion Ia would assume the shape ofa halftorus and the sheet would be subjected in the vertical direction only to forces dependent upon the small radius of the torus. However, in the present case of a conical skirt, despite this beading, the whole skirt retains a general frustoconical form ensuring its stability of shape under pressure and there is another stress in the vertical direction, as a result of the conicity, which assumes a maximum value at the top ofthe skirt, decreases towards the bottom and is cancelled out at the base of the skirt. Thus even in the case in which the sheet has a negligible resistance to elongation, the half-toroidal form of equilibrium will not be achieved, because of this vertical tension component, except in the case of the bottom panel. The lowest panel will be closest to the half-toroidal shape and the topmost panel will have a shape most remote from the half-toroidal. This form of equilibrium will in any case be a toroidal portion having a radius varying with the cushion pressure.

Disregarding the elasticity of the sheet in the vertical direction (and this is generally possible since the forces in the vertical direction due to the combination of the effects of the conicity and of the small radius of the torus remain very small compared with the horizontal forces) the length L of the sheet portion In contained between two hoops remains constant (FIGS. 3, 3a and 3b). When this sheet portion assumes a toroidal shape under the effect of the pressure, the two hoops therefore approach one another. The skirt is thus shorter under pressure than in the inoperative state, as will be seen from FIGS. land 2.

If the sheet has a negligible resistance to elongation parallel to the hoops with respect to the pressure level in question, in relation to that of the hoops, and a negligible elasticity in the axial direction the equilibrium shape of the skirt will therefore be reached at an infinitesimal pressure and will be maintained irrespective of the variations in this pressure.

Between the two extreme cases considered hereinbefore (and which have been explained only to simplify an understanding of the operation of the skirt), the invention provides a choice of a large number of intermediate solutions in which the entire mechanical strength in the peripheral direction is not provided either completely by the hoops or completely by the fluidtight sheet but is distributed to a certain extent between the hoops and the sheet. Because of its resistance to elongation the sheet will assume the toroidal equilibrium shape with more difficulty, and this necessitates an increase in its perimeter and each value of the internal pressure will give a toric arc ofa different radius and hence a different spacing between two consecutive hoops (see FIGS. 30 and 3b).

The height of the skirt will therefore vary with the pressure of the fluid cushion. It will be maximum at zero pressure (FIG. 1) and decrease when the pressure tends to increase (FIG. 2). The part of the skirt which will have the greatest variations in height will be the bottom part which is less subject to the additional influence of vertical traction forces due to the conicity.

This gives various advantages with the conical skirts according to the invention.

A first advantage is automatic dynamic stabilization of the skirt. Conventional conical skirts are subjected to a vibration involving the mass of fluid in the cushion when the machine is large. This phenomenon occurs when an increase in the cushion pressure coincides with an increase in the skirt volume such as is the case with conventional skirts of a fixed height which increase in diameter under pressure.

In the skirt according to the invention the diameter increase as a result of a pressure increase produces a very slight volume increase in relation to the considerable reduction in volume due to the vertical shrinkage of the skirt. Stability is therefore automatic and this skirt can be used to produce very large surface-effect machines.

Another advantage is an improvement of the machine suspension properties. When a surface-effect machine provided with flexible skirts passes at high speed over obstacles of elongate shape (e.g., sea swell), the conditions are such that it is as if the supporting surface were approaching or moving away from the base of the skirt. With a conventional skirt of a fixed height, the clearance (between the bottom of the skirt and the ground) passes very rapidly from a zero value to a maximum value such that the cushion is vented to atmosphere. This rapid variation in-pressure results in harmful hammer blows with regard to the strength of the skirt and the structure. The entire machine which has to follow irregularities in ground level is subjected to increasing vertical accelerations with increasing speed.

With the skirt according to the invention an accidental increase in ground clearance, while tending to reduce the cushion pressure, will result in an elongation of the skirt which will tend to resume its initial clearance height thus restoring the pressure to its initial value..Conversely, if there is an accidental reduction in clearance as a result of an obstacle, it will tend to increase the cushion pressure by the dynamic effect and the skirt will retract and will increase the clearance at the bottom of the skirt and decrease the pressure. Thus the mass of fluid contained in the skirt will act as a shock-absorbing buffer between the obstacle and the machine structure.

Since the part of the skirt which is capable of the greatest variations in height is the bottom part, the suspension has a variable flexibility capable of small deformations at the bottom of the skirt under small forces, and deformations with a greater rigidity for the remainder of the skirt in the case of considerable forces.

In this way, the skirt according to the invention, which produces an air pad of variable height between the surface of the ground (or the sea) and the machine structure, results in a reduction of the vertical accelerations produced by level variations at high speed. Also, since the bottom of the flexible skirt tends to follow the surface of the ground, the risk of the cushion being vented to atmosphere, followed by abrupt restoration of pressure, and hence hammer blows, are eliminated.

Another advantage of the skirt according to the invention is a considerable saving in mass.

The saving in mass obtainable with this skirt is due firstly to its suspension properties. Elimination or reduction of hammer blows in the mass of the cushion allows smaller sizes for the resistant elements.

The saving in mass is also due to the automatic dynamic stability properties of the skirt. The increase of the perimeter under the effect of the pressure is no longer harmful as in the case of a conventional conical skirt so that the resistant elements may undergo greater elongation and thus their dimensions may be smaller with the result that the skirt is less sensitive to impacts since it is more resilient.

In a conventional skirt having a homogeneous wall there is practically no intermediate between the main resistant elements and the mass of air in the cushion. Any aerodynamic hammer blow is instantaneously transmitted to these elements and results in instantaneous overload (impacts). In the skirt according to the invention the main resistant elements, i.e., the hoops, are tensioned by means of the sheet which, as a result of its elasticity, will absorb the energy before restoring the forces on the hoops, thus reducing instantaneous overloads and reducing impacts.

Experience has also shown that resistant microelements diffused throughout the skirt as in the case of the conventional skirt operate unsatisfactorily because it is impossible for adjacent elements to be subjected to the same tension so that only a proportion (e.g., 50 percent) of these elements is subjected to traction. When, according to the invention, the resistant elements (flexible hoops) are concentrated and arranged discretely, i.e., discontinuously, it is possible to use preformed strands (e.g., metal cables) of a suitable section, the mechanical characteristics of which are fully known. Since the cables are arranged with well-defined spacing and connected by a more resilient sheet or skin, the value of the forces applied to them are fully known.

The actual fluidtight wall of the skirt comprises few resistant filiform elements since all or most of the horizontal forces are taken by the hoops and the vertical forces are small, so that a minimum amount of flexible rubber can be used to coat them and provide sealing properties, and this is another appreciable factor in reducing weight.

These lightweight properties of the skirt according to the invention result in an additional improvement of the suspension because experience has shown that the value of accelerations perpendicular to the supporting surface and produced as a result of passing over obstacles increases with the weight of the skirt.

Another advantage of the skirt according to the invention is that its vertical folding is facilitated. The skirt of a ground effect machine must be able to fold vertically so that the structure can rest on the ground at standstill. Since the skirt according to the invention contains only very few diffused resistant elements it will be thin and hence very flexible and easy to fold. Since the main resistant elements are disposed horizontally and discretely they do not form any obstacle to vertical folding.

To obtain the maximum benefit from these advantages of the invention the structure of the skirt and the nature and arrangement of the hoops should be appropriately chosen according to the use for which the skirts are intended.

The sheet material forming the skirt wall, may, for example, consists of rectangular or other widths of cloth disposed horizontally or inclined at an angle of 45 or any angle, or cords in one or more layers disposed horizontally and vertically or crossing at any angles. These various arrangements allow selective regulation of the mechanical work required of the filiform resistant elements of fabrics or cords on the one hand and of the flexible rubber covering these elements and providing sealing properties on the other hand.

The flexible hoops may be metal cables or resistant elements of any other type, e.g., glass cables, cords based on natural or synthetic textiles, belts, fabric bands, and so on. The hoops can be connected to the diaphragm over their entire length or by spaced connections.

FIG. 3 shows another embodiment in which each hoop 3 consists of a cable secured between the diaphragm 1 and a fabric band 4 glued on to the latter. In FIG. 4, the cable 3 forming each hoop is secured in an extruded flexible profile 5 which is glued to the sheet I. l

The hoops of one skirt need not necessarily be identical nor need they be spaced uniformly. They may, for example, be made of cable of the same diameters and spaced unequally over the skirt or alternatively be spaced equally and be made from cables of different diameters. It is also possible to vary these two parameters jointly or group the cables in pairs or greater numbers. FIG. 5 shows hoops each made from two cables 3a, 3b, embedded in an extruded flexible profile 5a glued to the diaphragm 1.

The skirt according to the invention may be hooped over just part of its height. FIG. 6, for example, shows a skirt having a hooped portion 6 below a conical portion 7 of conventional construction. This gives a skirt of reduced deformation along the axis than does a skirt hooped from top to bottom. In FIG. 7, on the other hand, the portion 7a of conventional construction is situated below the hooped portion 6a in order to remove the hoops from the bottom of the skirt and prevent any damage to them by rubbing on the ground or on the surface of water. In FIG. 8, the conical portion of conventional construction 7b is situated below a cylindrical hooped skirt portion 617. bonding FIG. 9 shows an embodiment of the invention which gives a conical skirt 1 by providing hoops'by means of strips of resistant fabric 8. The cylindrical strips of fabric illustrated could be replaced by frusloconical strips.

FIGS. 10 to 14 show arrangements applicable to multilobed skirts.

In FIGS. 10 and 11 uniformly spaced points such as 9 of each hoop 3 are radially clinched by tie or stay means secured to the structure 2 of the ground-effect machine. Along the axis of the skirt the structure 2 supports a mount 10 from which a retaining cable 11 is suspended. A first series of main tie or stay means 12 connect the mount 10 radially to the uniformly spaced points 9 of one of the hoops 3. Uniformly spaced points 911 of another hoop, each situated in the same meridian plane of the skirt as one of the points 9, are also connected by a second series of main tie or stay means 13 to the retaining cable 11. Each of the main tie or stay means 12 or 13 consists of a cable which between its ends has an eyelet 14 through which a rigid element 15 passes (e.g., a rod or a tube) and secondary tie or stay means 12a or 13a extend above and below the eyelet 14 and consist of cables secured to the points 9b of the adjacent hoops which are situated in the same meridian plane as the fastening point 9 or 9a of the main tie or stay means. The length of the tie or stay means 12, 13 and 12a, 13a is adjusted so as to clinch the flexible hoops 3 in the uniformly spaced meridian planes of the points 9, 9a and 9b so that when the skirt is inflated it forms lobes 16 between said planes, said lobes being encircled substantially parallel (at 16a) to the supporting surface by the hoops 3. The hoops being clinched independently of one another can move freely towards and away from one another to allow toric deformation of the diaphragm under the action of the pressure inside the skirt.

FIG. 12 shows another embodiment of the clinching system. The fastening points 9 of the hoops which are situated in the same meridian plane are connected together by secondary cables 17 which are in turn connected by a web 18 to a main cable 19 secured at one end to the retaining cable 11 and at the other end to a mount 20 of the structure 2. The web 18 has a high resistance and a low elasticity in the radial direction (the direction of the double arrow 21) and is elastic in the perpendicular direction (direction of the double arrow 22), being made for example from filiform resistant elements disposed in the direction of the double arrow 21, enclosed in a sheet of elastic rubber. The shape of this web is such that when it is disposed flat as shown in the drawing the cables 17 and 19 are of parabolic shape. When the skirt inflates, this system provides clinching like the system shown in FIG. 10, the elasticity of the web in the vertical direction enabling the hoops 3 to move away from one another or towards one another depending upon the value of the internal pressure, while the cables retain their parabolic shape.

FIGS. 13 and 14 show an example of a system for fastening a clinching tie or stay means to a hoop consisting ofa cable 3. This cable is cut at its fastening point 9 and the cut ends are respectively fixed in bushes 23 and 23a having a fork 24, through the two arms of which a bore 25 extends. The end of a tie cable 26 is fixed in a bush 23b identical to the bushes 23 and 23a. The forks of the three bushes are pivotally connected to a plate 27 in the form of a rigid disc by means of pivots 28 pressfitted into the plate through bores. The bushes 23 and 23a pass through an aperture 29 formed in the wall of the skirt 1. This aperture is closed by resilient sheet 30 which is glued at 30a to the lips of the aperture and at 30b and 30c around the bushes 23 and 23a.

The invention increases the flexibility of multilobed skirts and facilitates most folding at the clinching means. In conventional skirts, clinching is provided by webs secured to the wall of the skirt and thus comprises the connection of three panels, namely two wall panels and one web panel. This connection forms a T-section which is very resistant to flexure and buckling, which makes it difficult to pass over obstacles and for the skirt to fold vertically.

In the skirts according to the invention, however, as will be seen in FIGS. 10 to 14, the tie cables clinching the hoops do not have these disadvantages,

I claim:

1. A yieldable skirting system for surface effect machines, comprising the combination of a close-contour fluidtight skirt wall of elastic structure which has substantial resilient extensibility radialwise upon exertion of internal fluid pressure on said skirt wall which is thereby peripherally stretchable to a substantial extent, and

a plurality of hoops fitted peripherally on and mutually spaced lengthwise of said skirt wall, said hoops being of a material which is relatively inextensible radialwise compared with said skirt wall upon such exertion of internal pressure thereon and being thereby peripherally unstretchable relatively to the peripheral stretchability of said skirt wall,

whereby said skirt wall, upon such exertion of pressure thereon, is caused to bulge between successive hoops with a part toroidal outline ofsmoothly curved shape.

2. Skirting system as claimed in claim 1, wherein said skirt wall is lobated in planform and comprises a succession of lobes extending around a longitudinal axis of said skirt wall and joined to each other along cuspidal edges, and said hoops are likewise lobated and comprise a like succession of lobes extending around said axis and joined to each other at cuspidal points located on said cuspidal edges.

3. Skirting system as claimed in claim 2, further comprising tie members attached to said cuspidal points of said hoops and extending inwardly of said skirt wall.

Claims (3)

1. A yieldable skirting system for surface effect machines, comprising the combination of a close-contour fluidtight skirt wall of elastic structure which has substantial resilient extensibility radialwise upon exertion of internal fluid pressure on said skirt wall which is thereby peripherally stretchable to a substantial extent, and a plurality of hoops fitted peripherally on and mutually spaced lengthwise of said skirt wall, said hoops being of a material which is relatively inextensible radialwise compared with said skirt wall upon such exertion of internal pressure thereon and being thereby peripherally unstretchable relatively to the peripheral stretchability of said skirt wall, whereby said skirt wall, upon such exertion of pressure thereon, is caused to bulge between successive hoops with a part toroidal outline of smoothly curved shape.

2. Skirting system as claimed in claim 1, wherein said skirt wall is lobated in planform and comprises a succession of lobes extending around a longitudinal axis of said skirt wall and joined to each otHer along cuspidal edges, and said hoops are likewise lobated and comprise a like succession of lobes extending around said axis and joined to each other at cuspidal points located on said cuspidal edges.

3. Skirting system as claimed in claim 2, further comprising tie members attached to said cuspidal points of said hoops and extending inwardly of said skirt wall.

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